anki crashes when anki-wiktionary plugin

Hi,

I've observed that if `anki-wiktionary` cannot find a word while bulk-filing a *single* note, it throws a meaningful error.
However, if it used on multiple nodes and one of them fails, the `anki` in its entirety just crashes w/o further errors.

I'm not sure how much this is `anki`s fault or this plugin, but maybe the error handling in that case should be done more subtly?

I'm happy to file a bug at `anki` if you think this cannot reasonably be fixed within `anki-wiktionary`. I'm currently not involved deeply enough to figure it out myself. And maybe it is trivial and was just overlooked :)

Reproduce bulk-filing multiple notes with an anki-wiktionary lookup that cannot find one word, then inspect the add-on's error handling around that operation. Done means a failed lookup is handled without crashing Anki and an appropriate error is reported; the issue names no files or tests to start from.

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